1. Field of the Invention
The present invention relates to an ophthalmologic apparatus that includes a mechanism for sliding a sliding substrate having an optical system unit, such as a fundus camera or an ophthalmoscope, on a horizontal plane.
2. Description of the Related Art
Conventionally, an ophthalmologic apparatus has been configured by mounting a sliding substrate, which can slide in forward/backward and lateral directions in response to an operation made by an operation stick, on a fixed base to which a face receiving portion for a subject is attached. In such an ophthalmologic apparatus, an optical system main unit is mounted on the sliding substrate via a vertical motion mechanism.
Japanese Patent Application Laid-Open No. 03-026228 discusses an ophthalmologic apparatus in which a guide tube and a guide shaft are arranged between a sliding substrate and a fixed base, so that the sliding substrate moves in a lateral direction with respect to the fixed base by sliding the guide shaft through the guide tube. Further, a pinion gear attached to both ends of the guide shaft engages with a rack that is arranged on either side of the sliding substrate. The sliding substrate on which the rack that engages with the pinion gear is arranged moves in a forward/backward direction with respect to the fixed base by rotating the pinion gear in synchronization with the guide shaft.
Further, a ball bearing is attached at a position near the pinion gear on either end of the guide shaft. The ball bearing allows the guide shaft to smoothly rotate by maintaining a gap that is suitable for the engagement between the pinion gear and the rack while supporting the weight of the sliding substrate via the guide face of the sliding substrate. In this case, the ball bearing acts as a mechanism for preventing the sliding substrate from lifting up from the fixed base by stopping a rack gear plate from lifting up from the guide shaft.
However, uplift of the sliding substrate from the fixed base is also caused by inclination of the guide shaft with respect to the guide tube attached to an upper portion of the fixed base. For example, when a subject's eye is to be aligned with the ophthalmologic apparatus, the sliding substrate may be moved in a lateral direction (axial direction of the guide shaft). In such a case, if the distance between the guide tube and the guide shaft's center of gravity increases, the difference in the moments acting on the two ends of the guide shaft increases. Consequently, the guide shaft is more likely to incline with respect to the guide tube.